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The diheme enzyme MauG catalyzes oxidative post-translational modifications of a protein substrate, precursor protein of methylamine dehydrogenase (preMADH), that binds to the surface of MauG. The high-spin heme iron of MauG is located 40 Å from preMADH. The ferric heme is an equilibrium of five- and six-coordinate states. PreMADH binding increases the proportion of five-coordinate heme three-fold. On reaction of MauG with H2O2 both hemes become FeIV. In the absence of preMADH the hemes autoreduce to ferric in a multistep process involving multiple electron and proton transfers. Binding of preMADH in the absence of catalysis alters the mechanism of autoreduction of the ferryl heme. Thus, substrate binding alters the environment in the distal heme pocket of the high-spin heme over very long distance. [ABSTRACT FROM AUTHOR]

Highlights: [•] LodA has a tryptophylquinone cofactor but functions as an oxidase not a dehydrogenase. [•] LodA exhibits a ping-pong kinetic mechanism with lysine and O2 as substrates. [•] The kinetic mechanism of LodA is consistent with a covalent lysine-CTQ intermediate. [ABSTRACT FROM AUTHOR]

MauG has been cocrystallized with methylamine dehydrogenase (MADH) with its TTQ cofactor in the o-quinol (TTQOQ) and quinone (TTQOX) forms and the structures of the resulting complexes have been solved. The TTQOQ structure crystallized in either space group P21 or C2, while the TTQOX structure crystallized in space group P1. The previously solved structure of MauG in complex with MADH bearing an incompletely formed TTQ cofactor (preMADH) also crystallized in space group P1, although with different unit-cell parameters. Despite the changes in crystal form, the structures are virtually identical, with only very minor changes at the protein-protein interface. The relevance of these structures with respect to the measured changes in affinity between MauG and various forms of MADH is discussed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A W199E MauG mutation alters hydrogen bonding interactions with preMADH. [•] A W199E MauG mutation alters the kinetic mechanism of interprotein electron transfer. [•] Trp199 of MauG plays multiple roles in MauG-catalyzed TTQ biosynthesis. [ABSTRACT FROM AUTHOR]

Abstract: MauG catalyzes posttranslational modifications of methylamine dehydrogenase to complete the biosynthesis of its protein-derived tryptophan tryptophylquinone (TTQ) cofactor. MauG possesses a five-coordinate high-spin and a six-coordinate low-spin ferric heme, the latter with His-Tyr ligation. Replacement of this tyrosine with lysine generates a MauG variant with only high-spin ferric heme and altered spectroscopic and redox properties. Y294K MauG cannot stabilize the bis-Fe(IV) redox state required for TTQ biosynthesis but instead forms a compound I-like species on reaction with peroxide. The results clarify the role of Tyr ligation of the five-coordinate heme in determining the physical and redox properties and reactivity of MauG. [Copyright &y& Elsevier]

X-ray exposure during crystallographic data collection can result in unintended redox changes in proteins containing functionally important redox centers. In order to directly monitor X-ray-derived redox changes in trapped oxidative half-reaction intermediates of Paracoccus denitrificans methylamine dehydrogenase, a commercially available single-crystal UV/Vis microspectrophotometer was installed on-line at the BioCARS beamline 14-BM-C at the Advanced Photon Source, Argonne, USA. Monitoring the redox state of the intermediates during X-ray exposure permitted the creation of a general multi-crystal data collection strategy to generate true structures of each redox intermediate. [ABSTRACT FROM AUTHOR]

Cyclopropylamine is a mechanism-based inhibitor of the quinoprotein methylamine dehydrogenase (MADH) from Paracoccus denitrificans. The resulting inactivation is accompanied by the formation of a covalent cross-link between the α and β subunits of MADH. The results of site-directed mutagenesis studies indicate that Phe55 on the α subunit is required for this process. No cross-linking is seen with αF55A or αF55I MADH mutants. In contrast, with αF55E MADH cross-linking of subunits is observed. These results suggest a novel mechanistic role for a phenylalanine residue and the possible importance of protein dynamics in this enzyme mechanism. [Copyright &y& Elsevier]